Structure and growth rate of Prosopis flexuosa woodlands in two contrasting environments of the central Monte desert

Abstract

In the temperate dry regions of Argentina (Monte desert), “algarrobales” are open woodlands dominated by woody species of the genus Prosopis, particularly Prosopis flexuosa D.C. For several centuries these woodlands have provided the local human populations with fuel, timber and food. At present, “algarrobales” show different degrees of degradation as a consequence of particularly intensive logging during the beginning of the last century. We selected two sites with different climatic conditions in the Central Monte Desert, the Telteca and Ñacuñán Reserves with total annual precipitation of 159 and 329mm, respectively. Accessibility to the water-table is different for both sites, as water-table is superficial (10–15m) at Telteca and deep at Ñacuñán (70m). In a first attempt to understand the dynamics of these woodlands, we compared the growth rate and the woodland structure of P. flexuosa on both sites. The structure of P. flexuosa populations was analyzed in eight and seven plots at Ñacuñán and Telteca, respectively. In each plot we estimated density, total coverage, total basal area, and number of stems per tree. The presence of annual rings in the wood of P. flexuosa trees allowed us to use dendrochronological methods to study the growth rate of these populations. Differences in population structure and growth rate between sites could be attributed to different water supply and anthropogenic disturbances. The faster rate of radial growth observed at the Telteca Reserve may respond to the presence of a near-surface phreatic layer. At this site, however, mean annual precipitation is lower than at Ñacuñán Reserve. At Ñacuñán, woodland structure reflects the impact of the intense logging activities carried out in the region in the early 20th century.